1901.] on Vitrified Quartz. 531 



aware, been unmistakably established. Therefore, it is interesting 

 to record the fact, first observed by Mr. Lacell, that nitric peroxide 

 is produced by heating a mixture of oxygen and nitrogen above 

 the melting-point of platinum in tubes of silica. It is easy to 

 obtain a gas showing a distinctly yellow colour and exhibiting the 

 reactions of nitric peroxide in this way. 



Of course, vitreous silica is not entirely without defects. Unfor- 

 tunately it becomes slightly permeable to hydrogen as platinum does, 

 though to a less extent, at about 1000°.* It is attacked when hot 

 by basic oxides. It may be heated to about 960°, in contact with 

 copper oxide without injury, but at higher temperatures it is attacked. 

 It may be heated more strongly with ferric oxide, but quicklime 

 attacks it at a bright red heat. It is evident that caution must 

 be exercised when it is in contact with basic oxides or alkaline solu- 

 tions. When one first fashions vessels of silica before the flame the 

 vessels exhibit to a greater or less extent a phenomenon resembling 

 the devitrification of glass. They become covered with a white 

 opaque crust. This is easily removed by reheating, provided that 

 the tube is kept scrupulously free from dust and dirt. If this pre- 

 caution be not taken the appearance of the vessel may be spoilt 

 permanently. The earlier observers attributed this phenomenon to 

 the volatility of silica. My impression is, that it is connected with 

 the minute traces of alkali metals which are present in most Brazil 

 pebble, and which are usually burnt off in the processes I have 

 described. 



What I have told you to-night has shown you that in several re- 

 spects vitrified silica is as much superior to the best glass, as Jena 

 glass is superior to more ordinary specimens, and that the progress 

 made during the last few years will enable investigators to employ 

 vitreous silica much more widely in the future than has been possible 

 in the past. At the same time it is evident that the processes for 

 producing it are still in their infancy, that there is much more to be 

 done, and that further progress can only be made at considerable 

 expense. 



In concluding my remarks I wish to express the great obligation 

 I am under to my friend Mr. Lacell. You will have discovered for 

 yourselves that the chief burden has been upon his shoulders to- 

 night, and that without the illumination provided by his precise 

 and beautiful manipulations my discourse would have been but a 

 dry affair. Also I must add that the cost of the work at its later 

 stages has been partly defrayed by a subsidy from the Government 

 Grant Fund of the Koyal Society. 



[W. A. S.] 



* Villard, Comptes Rendus, cxxx. 1752. 



2 n 2 



